1. Field of the Invention
The present invention relates to an exposure method and an exposure apparatus to be used, for example, when a mask pattern is transferred onto a substrate in the lithography step for producing, for example, semiconductor elements, liquid crystal display elements, plasma display elements, and thin film magnetic heads. In particular, the present invention relates to an exposure apparatus in which a vibration-preventive control is adopted.
2. Description of the Related Art
A high exposure accuracy is required for the exposure apparatus of the full field exposure type (stepper type) or the scanning exposure type (for example, those based on the step-and-scan system) to be used when the semiconductor element or the like is produced. Therefore, in the exposure apparatus, an arrangement, which makes it possible to perform highly accurate positioning or highly accurate scanning, is adopted for a reticle stage on which a reticle as a mask is placed and positioned and for a wafer stage in which a wafer as a substrate is placed and two-dimensionally moved respectively.
That is, the reticle stage for the conventional exposure apparatus of the scanning exposure type is arranged, for example, such that a frame-shaped coarsely movable stage, which is movable at an approximately constant velocity in the scanning direction, is placed on a reticle base, and a finely movable stage, on which the reticle is placed, is connected into the coarsely movable stage by the aid of an actuator which is used to perform positioning in a minute amount two-dimensionally. In this arrangement, the coarsely movable stage and the finely movable stage are slidably placed on the common reticle base by the aid of air bearings respectively.
Also in the case of the reticle stage for the conventional exposure apparatus of the full field exposure type, a driving unit such as a linear motor, which is used to drive a movable stage on which the reticle is placed, is installed on the reticle stage
On the other hand, in recent years, in order to enhance the throughput, a so-called double-wafer stage, which is provided with two movable stages, has been suggested as a wafer stage for the exposure apparatus. When the double-wafer stage is used, the throughput can be improved by performing exchange and alignment for a wafer on the second movable stage during a period in which exposure is performed for a wafer on the first movable stage. The conventional double-wafer stage has been constructed as follows in order to simplify the arrangement. That is, a guide for one axis of two orthogonal driving axes is commonly used by the two movable stages, or the two movable stages are independently driven by using plane motors.
Further, a system, which is based on the mechanical contact such that upward and downward movement is performed, for example, with a cam mechanism, is adopted for the driving system for a sample base (Z leveling stage) for performing leveling and focusing in the conventional wafer stage.
The conventional exposure apparatus has been assembled on a base plate which is installed by the aid of a plurality of (for example, four) vibration-preventive pedestals including air dampers in order to mitigate the influence of vibration from the floor. However, when an excimer laser light source is used as an exposure light source, some of members of the exposure light source and the illumination optical system are supported by support members different from the base plate. Recently, in order to allow other stage sections and other components to be not affected by the vibration generated in respective stage sections of the exposure apparatus, a system has been also suggested, in which a wafer base for supporting a wafer stage and a reticle base for supporting a reticle stage are supported mutually independently by a plurality of active type vibration-preventive units including air dampers and control units respectively.
Among the conventional exposure apparatuses as described above, as for the system in which the base plate is supported by the aid of the plurality of vibration-preventive pedestals on the floor, and the approximately entire mechanism of the exposure apparatus is placed thereon, the influence of the vibration between the respective stage sections is directly transmitted to the other stage sections especially in the case of the scanning exposure system. Therefore, it is feared that the exposure accuracy (for example, the transfer faithfulness such as the line width accuracy and the overlay accuracy) may be deteriorated. In the case of the system in which the reticle base and the wafer base are supported mutually independently by using the plurality of active type vibration-preventive units including the air dampers and the electromagnetic control units respectively, for example, the vibration having a low frequency from the floor tends to be independently transmitted to the both stage sections via the air dampers. Therefore, it is feared, for example, that any positional discrepancy concerning the low frequency may occur between the both stage sections.
In the case of the conventional reticle stage, the coarsely movable stage or the driving mechanism or the like for driving the movable stage (for example, the finely movable stage) is installed together on the reticle base. Therefore, the vibration, which is generated in the coarsely movable stage or the driving mechanism or the like, tends to be transmitted to the movable stage (reticle). For example, when the driving velocity of the movable stage is increased in order to enhance the throughput, it is feared that the positioning accuracy for the reticle or the accuracy of the scanning velocity or the like may be lowered. On the other hand, an inconvenience arises such that the throughput cannot be enhanced so much in order to maintain, for example, the positioning accuracy for the reticle to be within a predetermined range. Further, it is necessary to increase the rigidity of the reticle base in order to maintain a satisfactory flatness of the sliding surface for the movable stage, because the movable stage or the driving mechanism or the like is installed together on the reticle base. As a result, an inconvenience arises such that the exposure apparatus becomes large in size, and the weight is increased as well.
Taking the foregoing points into consideration, a first object of the present invention is to provide an exposure method and an exposure apparatus in which the influence of vibration is mitigated, and a high exposure accuracy is obtained.
A second object of the present invention is to provide an exposure method and an exposure apparatus provided with a reticle stage capable of controlling a movable stage at a high velocity and with a high accuracy without increasing the load on a reticle base, in which the influence of vibration on the side of a driving mechanism is mitigated.
Another object of the present invention is to provide a production method which makes it possible to efficiently produce the exposure apparatus as described above, and a method for producing devices, which makes it possible to produce a highly accurate device by using the exposure method as mentioned above.